Adapter systems of this type are used nowadays in virtually every motor vehicle for the installation of the car radio. The dimensions of the installation space are usually oriented in this case to DIN ISO 7736 which also proposes possibilities for fastening the built-in device in the installation space. A “front fastening” and a “lateral fastening” are preferred, in which elastically resilient projections, which are provided in each case at regular intervals on the adapter system, latch into recesses, which correspond thereto, on the surfaces bounding the installation space. In addition, a rear fastening can take place by means of a threaded bolt. The new digital generation of tachographs is no longer, like the mechanical predecessors, accommodated in a round installation form in the motor vehicle but rather in an installation space according to the abovementioned standard. Firstly, known adapter systems for the installation in installation spaces of this type, in particular for car radios, are complicated and cost-intensive to produce as a punched and bent part due to the dimensions and tolerances and, in addition, are only of limited suitability for the mounting of the complicated and sensitive tachographs. Furthermore, due to the dimensions of the device, the installation of the digital tachograph by means of a known adapter system would render the rear fastening, which is actually optional, indispensable, thus unduly increasing the outlay of assembly.